1. Technical Field
The present invention relates to a method for designing a spectacle lens to be mounted in a spectacle frame having a large bend angle such as a wraparound type spectacle frame.
2. Related Art
In recent years, a spectacle frame of the wraparound type has become popular, especially as sports sunglasses. The spectacle frame of the wraparound type has a characteristic that, since the spectacle frame of the wraparound type has a large bend angle to bend around a face, even the sides of the face are covered by lenses and the field of view is wide. Therefore, a spectacle frame of the wraparound type is popular among athletes as a frame for safety spectacles used during sports and for general eye protection.
The wraparound type spectacle lens is provided with an optical convex surface on an object side and an optical concave surface on an eye side and is mounted in the spectacle frame in a manner tilting with respect to a line of sight (JP-A-2005-284059).
The optical concave surface of the spectacle lens is prescribed for near-sightedness correction, far-sightedness correction or the like depending on eyesight of a user. Thus, spectacle lenses are typically designed in variation, but spectacle frames in which the spectacle lenses are mounted are often standardized.
Typically, a spectacle lens is mounted in a spectacle frame using an outer shape of the spectacle frame as a reference. Specifically, a spectacle lens is mounted in a spectacle frame so that an optical convex surface on an object side conforms to the outer shape of the spectacle frame.
In a spectacle lens, light that enters from the object side refracts at the optical convex surface and linearly travels in the lens, before the light retracts again at the optical concave surface and enters a pupil of a user.
Since the optical concave surface on the eye side is prescribed in correspondence with eyesight or the like of a user, the surface differs from one lens to another.
A typical spectacle lens is mounted in a spectacle frame using only the outer shape of the spectacle frame as a reference. Thus, a prescription made on the optical concave surface on an eye side may cause the optical concave surface to form an inappropriate angle with respect to the spectacle frame.
When the optical concave surface tilts relative to the appropriate angle, an average dioptric power error, an astigmatic aberration, and a prismatic error occur. A user may suffer eyestrain or the like due to such errors.